JPH03281060A - Method for controlling prevention to flow-out of slag in ladle - Google Patents

Abstract

PURPOSE:To utilize the maximum amount of molten metal without flowing out slag by descending a bar-like body synchronizing to descending velocity of molten metal surface and plugging a molten metal discharging hole with flow-out rate adjusting means after reaching the body upper part of the molten metal discharging hole. CONSTITUTION:Position of the bar-like body 18 when it reaches the upper part of molten metal discharging hole 12 is checked, and by ascending from this position to the prescribed height, the relation between the position of bar-like body 18 in order to obtain timing plugging the discharging hole 12 and the position at the upper part of discharging hole 12 is always kept to the constant regardless of the eroded condition. Further, the timing closing the sliding nozzle 14 does not only depend on variation of balancing force, but also absolute value of holding force. Therefore, in the case the variation is difficult to detect, by varying flowing of the molten steel 10, the sliding nozzle 14 can be surely made to close. The bar-like body 18 is descended synchronizing to the descending velocity of molten metal surface, and after reaching to the discharging hole 12, by closing the discharging hole 12 with the flow-out rate adjusting means 14, the flow-out of slag is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a method for preventing slag from flowing out in a ladle to prevent slag from flowing out together with molten steel when molten steel is taken out from below a ladle filled with molten steel. Regarding the control j11 method.

[Conventional technology]

As is well known, in the steelmaking process, the refined molten steel in the ladle is poured into the continuous casting tundish by opening a sliding nozzle through the tapping hole provided at the bottom of the ladle, and then poured from the tundish into the mold to form a slab. is manufactured. In the process of pouring molten steel from the ladle mentioned above, what is important in producing clean steel is to prevent the slag floating on the self-molten steel in the ladle from flowing out. This is where efforts are being made.

The outflow of slag when pouring molten steel from the ladle to the tundish is caused by (1) entrainment of the floating slag layer in the vortex that occurs directly above the ladle tap hole as the molten steel level in the ladle decreases;
and (2) outflow of the floating slag layer due to a delay in determining the end of ladle injection. Therefore, (1) and (2) above
), a method for preventing slag outflow has already been proposed in Japanese Unexamined Patent Publication No. 60210352.

This method is called the floating valve method, and when the molten steel level in the ladle decreases and a vortex is generated, a floating valve whose specific gravity is adjusted is applied to the slag-molten steel interface on the tapping hole surface. The idea is to prevent the floating slag from flowing out by placing the floating valve in position to prevent the generation of eddies and slag entrainment, and at the end of injection, the floating valve lands on the tap hole to close the tap hole and prevent floating slag from flowing out.

According to this technology, the generation of vortices can be effectively prevented and the entrainment of slag can be effectively prevented.
The effect of preventing slag outflow at the end of injection is not sufficient. In other words, if the refractories near the ladle tap hole and the refractories constituting the floating valve are eroded and their shapes change, the tap hole cannot be reliably blocked and slag will flow out at the end of pouring. There are often cases where

To solve this problem, JP-A No. 62-203667 discloses a method in which a float is placed at the interface between the slag layer and molten steel and lowered to follow the drop in the molten metal level to a predetermined height. The descent is stopped at that point, and the subsequent change in the float's buoyancy is detected as a change in the float's tension.
Based on this, a method of blocking the tap hole of the ladle is disclosed.

[Problems to be Solved by the Invention] In the present invention, the timing of closing the tapping hole is determined based only on changes in the tension applied to the float held at a predetermined height. Therefore, when the refractory near the tap hole changes its shape due to melting damage, the positional relationship between the top of the tap hole and the detection location changes, changing the state of the flow of molten steel and causing a timing shift. In addition, the state of the flow of molten steel changes depending on the state of thermal convection of the molten steel or the opening degree of the tapping hole, causing variations in the measured tension values, making it difficult to judge whether there is a sudden change, and as a result, there is a blockage. Sometimes the timing is wrong.

Therefore, an object of the present invention is to provide a slag outflow prevention control method that improves the above points.

[Means to solve the problem]

The gist of the present invention is as follows.

(1) A ladle l having a tapping hole 12 at the bottom and an outflow amount adjusting means 14 for adjusting the amount of molten steel flowing out from the tapping hole 12.
A method for preventing the outflow of slag from O. i) After the rod-shaped object I8 is held above the molten metal surface, when the rod-shaped object 18 is preheated and plunges into the molten steel, the adhesion of slag and molten steel is prevented. After the hot water level has fallen to a height that allows sufficient time to prevent the melt from forming, the rod-shaped object 18 is lowered and held above the hot water surface to prevent 11) slag and molten steel from adhering when entering the molten steel. 1ii) After the hot water level has decreased to about the vertical length of the rod-shaped object 18, the rod-shaped object 18 is lowered. iv)
After the suspension force of the rod-shaped object 18 reaches a predetermined value less than the value obtained by subtracting the buoyancy of the molten steel from the weight of the rod-shaped object 18, the rod-shaped object 18 is assumed to have reached the upper part of the tapping hole 12, and the descent is stopped. After measuring the current position of the rod-shaped object 18, the rod-shaped object 18 is raised to a predetermined height and held. force W, and the fishing support force W just before the slag flows out,
The relationship of ΔW, which is the difference between When the position of the rod-shaped object 18 suddenly changes before reaching the fishing support force W immediately before the slag outflow, which is determined by -Wo-ΔW, the rod-shaped object 18, vi) or before the weight of the rod-shaped object 18 suddenly changes, iv) the position of the rod-shaped object 18 when it reaches the tapping hole 12, and the above V) regression formula, W 1 = W o - ΔW When the fishing force WI just before the slag outflow is reached, the rod-shaped object 1 is moved at a speed that is in line with or faster than the lowering speed of the molten metal surface.
vi) After the rod-shaped object 18 reaches the upper part of the tap hole 12, the tap hole 12 is closed by the outflow amount adjusting means 14.

[Effect]

In step iv), the position of the rod-shaped object when it reaches the top of the tap hole is known, and by rising from that position to a predetermined height, the position of the rod-shaped object and the top of the tap hole are determined in order to obtain the timing to block the tap hole. The positional relationship between the two is always kept constant regardless of the state of erosion.

Furthermore, the timing of closing the sliding nozzle depends not only on changes in the fishing support force but also on the absolute value of the fishing support force. Therefore, even if the change in the flow of molten steel is difficult to detect, the sliding nozzle can be reliably closed. If bare metal or slag adheres to the rod-shaped object, it will cause disturbance and be affected, so in step ii), preheating is performed to prevent adhesion as much as possible when it enters the molten steel. Further, even if deposits adhere to the rod-shaped object due to insufficient preheating, the preheating sufficiently melts and removes the deposits without causing any problems.

In order to detect the state of melting loss, the rod-shaped object in the present invention is composed of a metal that is sufficiently heavier than molten steel and a refractory covering it, and the total specific gravity is set to be sufficiently larger than that of molten steel. . Therefore, the rod-shaped object does not float near the surface of the molten steel. Moreover, its length is designed to be longer than the molten metal level at which the vortex is generated, and when the molten metal level falls below this length, it is submerged in the molten steel in step iii), so a part of the molten steel is always kept in the molten steel. It protrudes from the surface, preventing the generation of eddy currents.

In addition, in order to reduce the cost of the rod-shaped object, the length of the rod-shaped object is shortened, and vortices are prevented by immersing a part of the rod-shaped object in molten steel near the hot water level where eddy currents occur.
When the hot water level becomes less than the length of the rod-shaped object, ii
i) The same effect can also be obtained by performing the following operations.

In steps vi) and vi), the rod-shaped object is lowered in synchronization with the descending speed of the molten metal surface, and after reaching the upper part of the tap hole, the tap hole is closed by the outflow amount adjusting means (sliding nozzle) to remove the slag. It becomes possible to make maximum use of molten steel without causing it to flow out.

In order to more reliably prevent the slag from flowing out, the descending speed of the rod-shaped object may be made faster than the working speed of the molten metal surface. In this case, the molten steel is slightly degraded, but it is not at a level that poses a problem.

〔Example〕

FIG. 1 is a diagram showing a device for preventing slag outflow in a ladle according to the present invention. A sliding nozzle 14 is provided in the middle of a long nozzle 12 provided at the bottom of the ladle 10,
The amount of outflow of molten steel 16 in ladle 10 is adjusted. 17 represents a slag layer. A rod-shaped object 18 suspended above the long nozzle 12 by a wire 28 is hoisted up and lowered by a winch 32 rotated by the rotation of the motor 20, thereby moving up and down above the long nozzle 12.

A load cell 24 is provided in the middle of the wire 28, and the tension of the wire 28 is measured. The pulse generator 22 generates pulses in response to the rotation of the winch 32, and by counting these pulses, the vertical position of the rod-shaped object 18 is measured. Pulses from the pulse generator 22 and signals from the load cell 24 are input to a sequencer 30,
Motor 20 and sliding nozzle 14 are controlled according to signals from sequencer 30. 26 also represents a pot lid. During preheating, the rod-shaped object 18 is set between the pot M26 and the slag layer 17, and is naturally preheated by the atmospheric temperature inside the pot.

Note that, in order to prevent damage due to overheating, it is preferable to provide piping for passing a cooling medium around the load cell 24 and the wire 28.

Further, a function for adjusting the positions of the long nozzle 12 and the rod-shaped object 18 may be provided above the wire 28, but this is not necessary since the ladle 10 is normally set at approximately a predetermined position.

FIG. 2 is a diagram for explaining a method of controlling the apparatus shown in FIG. 1. Further, FIG. 3 is a flowchart of control of the sequencer 30. An example of the control method according to the present invention will be described with reference to FIG. 1, as well as FIGS. 2 and 3.

When the ladle lO containing the molten steel 16 is installed at a predetermined position, the sliding nozzle (SN) 14 is opened to start taking out the molten steel, and the arm 34 is rotated so that the refractory stopper 18 closes the nozzle. It is located above 12. After waiting for a predetermined time and waiting for the hot water level to drop to the level shown in FIG. 2(a) (step a in FIG. 3), the stopper 18 is lowered to the preheating position shown in FIG. 2(a) and held there. (Step b in Figure 3). After a predetermined period of time has elapsed, the fishing support force, which is the value indicated by the load cell 24, is stored as W. When the hot water level drops to a predetermined value, for example 700 m (step C in Figure 3), the stopper 18 is lowered at a speed sufficiently faster than the lowering speed of the hot water level (step d in Figure 3), and the value indicated by the load cell 24 is lowered. When the weight of the stopper 18 decreases to less than the value obtained by subtracting the buoyancy of the molten steel (Fig. 3, step e), it reaches the upper part of the nozzle 12 and stops descending. The vertical position at the time is memorized.

Additionally, the level at which vortices occur in molten steel is generally 500 m.
++, and the aforementioned 700III11 is at a sufficiently higher level than this.

Next, the stopper 18 is 3
0 to 100 and is maintained (Figure 2 (C), 3
In step g) in the figure, the upward stroke at this time needs to be within a range that does not impede the pouring speed from the ladle.

CASEI (In the case of step h2 → step j in Figure 3) The value W from the load cell 24 is continuously monitored, and if there is a sudden change, it is assumed that the interface between the slag and molten steel has reached near the lower end of the stopper 18 (step After that, the stopper 18 is lowered at a speed equal to or faster than the lowering speed of the hot water level (FIG. 2(e), step h2→j in FIG. 3). When the stopper 18 reaches near the zero point in the vertical direction (step k), the sliding nozzle 14 is closed and the removal of the molten steel is completed (FIG. 2(f)).
Figure 3 Step 1).

FIG. 4(a) shows the actually measured value of the load cell value W when the operations shown in FIG. 2(a) to (d) are performed.

The period indicated by A is the preheating state shown in FIG. 2(a). The period indicated by B is the period during the descent from FIG. The period indicated by C is the rising period from the position shown in FIG. 2(b) to the position shown in FIG. 2(C). Thereafter, as the hot water level decreases, the buoyancy decreases and W gradually increases. W suddenly changes at the point indicated by D, which corresponds to the state shown in FIG. 2(d). E represents the timing at which the sliding nozzle started to close.

FIG. 5(a) is an enlarged view of the vicinity of E in FIG. 4(a).

As shown in the figure, after this sudden change, the sliding nozzle is normally closed to complete the injection of molten steel. Therefore, when a sudden change is confirmed, the rod-shaped object is lowered, and after reaching the upper part of the tapping hole, the sliding nozzle is closed, thereby preventing the slag from flowing out.

The reason for the sudden change in W is that, as shown in FIG. 6(a), right before and after the slag 17 on the molten steel 16 flows under the screen, contraction occurs, especially immediately after the slag 17 flows under the screen, and rod-shaped objects A gap suddenly appears around 18. This void causes a local decrease in buoyancy and a rapid increase in W.

The present invention utilizes the above phenomenon.

CASE 2 (In the case of step hl → step j in Figure 3) As shown in Figure 4 (b) and Figure 5 (b),
), unlike the case in Fig. 5(a), the rod-shaped object 18 and the melt m
There are cases where there is a large deviation of the outlet (molten metal tap hole), and cases where there is no sudden change in the suspension force W of the rod-shaped object 18 due to disturbances such as changes in the flow of molten steel. As a relationship that is effective in dealing with such a case, the position when the rod-shaped object 18 reaches the upper part of the molten steel outlet (tapping hole) and the suspension force W immediately before the rod-shaped object 18 plunges into the molten steel.

and the difference between the fishing support force W1 just before the slag flows out ΔW=(We
It was found that there is a correlation as shown in FIG. 7 with W+). This relationship becomes even higher by matching the steel types and the molten steel outflow speeds from the molten steel outflow ports of the ladle. Therefore, if there is no sudden change in the suspension force W of the rod-shaped object 18, the relationship shown in FIG. The fishing support force W immediately before the slag flows out is actually measured, and a regression equation is calculated between it and ΔW, which is the difference between the fishing support force W and the fishing support force W before the molten line enters. Using this regression equation, ΔW is calculated when the position of the rod-shaped object reaches the upper part of the molten steel outlet (tapping hole) is detected, and the fishing force WI just before the slag flows out is W1 = W0 - ΔW It can be predicted by calculating.

In this case, when the supporting force W reaches Wl, the rod-shaped object is lowered, and after reaching the upper part of the tapping hole, the sliding nozzle is closed to complete the injection of molten steel without preventing slag from flowing out. be able to.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the generation of vortices and the outflow of slag, and
By accurately grasping the timing of slag outflow, the yield can be improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the implementation device of the present invention, Fig. 2 is a diagram for explaining control for preventing slag outflow, Fig. 3 is a flowchart of the process, and Figs. 4 (a) and (b) are Figures 5 (a) and 5 (b) are enlarged views of a portion corresponding to Figure 4 (a), and Figure 6 (a) are diagrams showing changes in load cell value W over time in the method of the present invention. , (I)) are diagrams showing before and after the slag flows out under the screen, and FIG. 7 is a diagram showing the relationship between the position of the rod-shaped object when it reaches the tapping hole and ΔW. In the figure, 1O...Ladle, 12...Long nozzle,
14... Sliding nozzle, 16... Molten steel, 17... Slag, 18...
...Stopper, 22...Pulse generator 24...
・Load cell. Figure 1 Figure ((2) Lowering the throne Figure 4 (b) M-opening Figure 5 (,2) (b) Figure 6 (4) Cb) Figure 1 Arrival - Jisha position) - + Enter

Claims (1)

[Claims] (1) A ladle 1 having a tapping hole 12 at the bottom and an outflow amount adjusting means 14 for adjusting the amount of molten steel flowing out from the tapping hole 12
This is a method for preventing slag from flowing out from the molten steel, and includes: i) After the rod-shaped object 18 is held above the molten metal surface, when the rod-shaped object 18 is preheated and plunges into the molten steel, the adhesion of slag and molten steel is prevented. After the molten metal level has fallen to a level sufficient to ensure sufficient time to prevent this, the rod-shaped object 18 is lowered and held above the molten metal surface, ii) to prevent slag and molten steel from adhering when entering the molten steel. After a sufficient period of time has elapsed for the rod-shaped object 18 to be
_0 is memorized, iii) After the hot water level has decreased to about the vertical length of the rod-shaped object 18, the rod-shaped object 18 starts to descend, and iv)
After the suspension force of the rod-shaped object 18 reaches a predetermined value less than the value obtained by subtracting the buoyancy of the molten steel from the weight of the rod-shaped object 18, the rod-shaped object 18 is assumed to have reached the upper part of the tapping hole 12, and the descent is stopped. After measuring the current position L of the rod-shaped object 18, raise it to a predetermined height and hold it; Force W_0 and fishing support force W just before slag outflow
The relationship of ΔW, which is the difference between =W_0−Δ
When the weight of the rod-shaped object 18 suddenly changes before reaching the fishing support force W_1 just before the slag outflow determined by W, the rod-shaped object 18 is lowered at a speed equal to or higher than the melt level lowering speed, vii) Or, before the weight of the rod-shaped object 18 suddenly changes, iv) the above v) immediately before the slag flows out as determined by W_1=W_0-ΔW using the regression equation with respect to the position L when the rod-shaped object 18 reaches the tapping hole 12. When the supporting force W_1 of molten metal is reached, the rod-shaped object 18 is lowered at a speed equal to or higher than the lowering speed of the hot water level, and viii) After the rod-shaped object 18 reaches the upper part of the tap hole 12, the outflow amount is A control method for preventing slag outflow in a ladle, characterized in that a tapping hole 12 is closed by an adjusting means 14.